Bronze vs Cast Iron valve guides

All
After comments in another thread about cast iron valve guides I thought it may be better for a new thread and get some discussion on the subject.

About 8 years ago I did a rebuild that involved new head castings. My local bike shop recommended I run the bronze guides. They don't usually don't work on anything much older than shovelheads but said they worked well in them. I went with them. At first the bike ran OK but after about 3000 miles started skipping very badly after the bike got hot. Engine had obvious valve lash. I could pull over cut it off to cool and in a few minutes hear a definite snap noise. As soon as the snap noise the bike ran fine until it got hot again. I pulled it apart to find the valve stems scarred. The valves had been hanging in the guides. This was the snap noise, valve cooling enough to loosen up in the guide. Also the tin cups were loose under the guides. The fiber washers under the cups had come apart. This also caused a pretty bad oil leak. I went back with more bronze guides reaming them looser. I also used a different fiber washer under the tin cup. The bike has run well since. It now has about 15000 miles on the engine. Only problem is the oil leak. I don't expect this old iron to be leak free but at times it looks like I am spraying for mosquitoes. I put some florescent dye in the oil and ran it to pinpoint the leak. It all seems to be coming from under the exhaust tin cups.

I will most likely pull it back apart soon but wanted some discussion about the material of guides and valves before that.

I was also thinking about the possibility of putting an o ring under the guide to seal the guide to the tin cup. It would take machining a groove on the underside of the guide and a high temperature o ring. Either this or machining the bottom valve spring seat to accept an o ring between the seat and guide where it meets the tin cup.

A good high silicone cast iron is the best. I usually make mine from either Ford Tractor guides or Cat guides.
Dusty

Cast iron is the only way to go in an aircooled cast iron head. That snap you heard is the guide letting the valve retun to it's normal postion from the seized postion. It probably raised the guide off the head, therefore taking out the gasket between the head and tins. Since Ed Rowe retired, I'm sure a lot of people would be interested in what tractors' guides your using Dave.
Thanks
Steve

I bought a couple of sticks of g2 self lubricating cast iron stock from Chicago Tubing about 15yrs ago. Still have about 5 ft left. It's nice to have in emergency situations, but making guides individualy is not cost effective when you can easily purchase them. Kibblewhite Precision Machine has high quality cast iron guides in a full range of sizes for Knuckles.

ncmc47
I'm sure you are correct about the snap noise. Why would this make the guide back out of the head? If this has happened again it would explain the oil leaking from under the tins.

amklyde
I looked at the Kibblewhite web site. Do their Black diamond valves work well with their guides? The guides I am running now are Kibblewhite bronze. They are several years old. Is the stem binding in the guide the only problem with bronze guides? Is this due to different expansion rates?

Thanks for the help
F

When it happened to me the valve seized tight to the guide, and had to drive it out. The piston probably hit the valve and since it was seized lifted the guide some what from the original postion. Cooling off had no effect since it was seized so hard. That's my story and I'm sticking to it. LOL Mine was the rear exhaust, had no trouble with the other guides although were also silicon bronze. Ed Rowe called me while on vacation and made things right, by replacing all the bronze guides I had with cast iron. We need more people with his ethic in the busness.
Steve

Steve
Thanks for the info. I'll probably go with the Kibblewhite valves and guides. I am still toying with the idea of cutting a grove in the bottom of the guide for a high temp o ring. There is plenty of metal and it would add some assurance of a good seal. Whatever it'll have to wait a little while.

F

What amt. of clearance between valve stem and guide are you guys running with cast iron guides?
Thanks.

I ran on the tight side of what's in the manual, which off the top off my head is .004-.006. But I would double chec that as my memory isn't what it used to be.
With bronze guides I ran .006 an it still seized. Brone has an expension coeffience about double of cast iron, thus the problem of bronze on the street.
Steve

I set them up with .0025 intake .0035 exhaust. I shorten and size the top of the guide for metal case Viton seals. The guides are sized with a ream to about .001 under and then finished with a Sunnen hone.

So ,You must shorten guide the thickness of the seal? and are you running seals on both in.& ex.
Thanks.

I remove about .165 for the blue Viton seals I am currently using, ( Anybody know where I can buy the DSI type seals?) but keep in mind if you are running a high lift cam you may need more for seal to lower retainer clearance.